Distinguishing water conservation from water savings in the western USA

Abstract

Chronic water shortages are a serious and growing concern in the western USA. Water conservation is among the key strategies promoted to help affected communities bring their water demands into better balance with current and projected supplies. The term ‘water conservation’, however, has different meanings to different people at different times, and the muddled and inconsistent interpretation of associated terms – including ‘water efficiencies’, ‘water savings’, and ‘water use’ – can confuse and even impede progress towards intended conservation goals. The importance of evaluating proposed water conservation measures by considering the relevant water pathways, the basin-scale water balances, and applicable water law is discussed, and assessments of several typical water conservation actions are provided as examples. To help planners and policy-makers ensure that proposed water conservation measures are likely to achieve desired conservation objectives, this paper identifies the key aspects to take into account when evaluating specific water conservation strategies and options.

Keywords:

• Water conservation
• water law
• water balance

Acknowledgements

The author thanks Laura Belanger, Jon Altenhofen, Michael Davidson, Drew Beckwith, and Thomas Econopouly for their reviews and helpful comments on an early draft of this document.

Notes

†The views expressed in this article are those of the author, and do not necessarily represent those of the Bureau of Reclamation, the US Department of the Interior, or the US Government.

Water law in arid- and semi-arid regions of the western USA is dominated by the doctrine of prior appropriation. That doctrine holds that the first party to routinely put water to a recognized beneficial use can claim a priority right to continue diverting water for those purposes that must be satisfied ahead of later appropriative claims, regardless of whether later ‘junior’ rights are located upstream or downstream. Conditions are placed on the manner, location, and extent to which the corresponding right to use water may be exercised, which often includes limitations on the re-use of that water, as well as limitations on what qualifies as a ‘beneficial use’. See, for example, Neuman (1998).

See, for example, Corbridge and Rice (1999), for a discussion of these terms in the context of State of Colorado water law.

The concept of ‘consumptive use’ is central to much of water administration under the western US priority appropriation systems. For example, the sale or transfer of water rights associated with an historic irrigation water use is typically determined on the basis of transferable consumptive use. Water that historically was diverted but not consumptively used is typically considered part of the general basin supply, and not available for sale or transfer.

While substantial legal hurdles remain in many western states, the water-management flexibilities and economic benefits that can be realized by incentivizing the transfer or lease of reduced consumptive use is not lost on state water administrators. For example, the State of Colorado is currently reviewing procedures and developing protocols to streamline annual leasing of reduced consumptive use achieved through on-farm deficit-irrigation and fallowing practices to new uses such as municipal supply and instream environmental flows (Colorado Water Conservation Board 2013).

For example, Table 7 of a report by McDaniels (1960) estimates a median of 22.6 inches (57.4 cm) annual consumptive use among 24 cotton-growing zones in Texas, with a range of 18.8–35.3 inches (47.8–89.7 cm). At a contemporary yield of around 672 kg of cotton per hectare, 5740 m³ of water per hectare would equate to about 3860 litres per pound of cotton. That said, determining the net consumptive use represented by growing cotton also should consider – and where appropriate, back out – the consumptive use associated with the vegetation (if any) that otherwise would be growing on the site.

Due to the often considerable time lag associated with the migration of groundwater to surface water outlets, this activity may in fact produce a short-term increase in a basin's surface water yield. Over the long term, however, that increase is not sustainable, unless consumptive use is reduced. Changes in the quantity and timing of return flows also may have consequences from a water law and water administration perspective; for a discussion of this topic, see National Research Council (1992).

While it may benefit the quality of water for downstream water users to reduce the quantity of salts leached from soils, the leaching benefits provided by an intentional surplus application of irrigation water represent an essential farm irrigation practice in many locations where saline soil conditions prevail.

As an example, consider a municipality of 100,000 residents that successfully reduces indoor water use by 20%. Assuming an average 265 liters per day of per-capita indoor use (Mayer and DeOreo 1999), and assuming that 5% of that is lost to consumptive use, the net realized reduction in consumptive use would be about 97,000 m³ annually (79 acre-feet). Where annual precipitation is less than 45 cm, an equivalent reduction in consumptive use could be achieved by ceasing water deliveries to no more than 15 hectares of irrigated cornfields or turf grass.